Genetic evaluation of dairy cattle using test day yields
2006
Zutere, R.
Genetic evaluation of dairy cattle for milk production based on 305-day lactation yields was compared to the evaluation based on the corresponding test day (TD) yields from the first lactation. The heritability estimates were 0.19, 0.13 and 0.15, respectively for milk yield, fat yield and protein yield, and these parameters are lower than the corresponding ones for the routine genetic evaluation with the lactation model in Latvia. The results of estimated breeding values (EBV) and relative breeding values (RBV) showed relatively high variance for all traits: higher for fat yield and lower for protein yield. The calculation of reliabilities showed that the use of test day model gives higher reliabilities of the estimated breeding values. The reliabilities are higher (about 2 - 4 %) for all traits using TD model on average for all animals and cows. For bulls group with calculated reliabilities of breeding values of at least 50 % for all traits, the measure of accuracy is higher with TD model from 7% for protein yield to 17% for fat yield. The ranking of the best Top 10 sires by TD model is similar to the lactation model. A total of 3 bulls for fat and protein yield are included in rankings of Top 10 both by TD and lactation models. TD yields could be used instead of 305-day yields for the genetic evaluation of dairy cattle. It helps to improve the accuracy of genetic evaluation and does not change ranking of the best sires drastically.
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